Wood chipper



June 14, 1955 R. R. ALEXANDER 2,710,635

WOOD CHIPPER Filed Feb. 20, 1953 2 Sheets-Sheet 1 INVENTOR.

June 14, 1955 R. R. ALEXANDER 2,710,635

WOOD CHIPPER r Filed Feb. 20, 1953 2 Sheets-Sheet 2 M figa INV NTOR.

" 2 5 0 lax 2,710,635 Patented June 1 2, 1955 woou cnnrnu Ronald R.Alexander, Nashua, N. EL, assignor to Improved Machinery, Inc., Nashua,N. EL, a corporation of Maine Application February 2% 1953, Serial No.337,992

4 Claims. (Cl. 144-462) This invention relates to wood chippers and moreparticularly to a novel chipper of the drum type adapted for cuttingwood chips from pulpwood or other stock for use in, for example, papermanufacture.

Wood chippers of the drum type have a number of advantages over diskchippers, the primary ones being uniformity of knife velocity, andsubstantially smaller size and weight. The latter is particularlyimportant in portable chippers, which are being used more and more dueto the economies inherent in the handling and transporting of wood inchip rather than log or bolt form.

Heretofore, however, drum chippers have suffered from a number ofdefects, the most important of which was their inability to produce highquality chips of uniform fiber length such as are essential in themanufacture of paper pulp, and this was particularly true when operatingdrum chippers at high speed. Hence, such drum chippers have found littleuse in the pulp manufacturing industry, in spite of their known inherentadvantages of constant knife speed, as well as light weight and smallsize.

I have found that the inability of heretofore known 5 chippers toproduce suitable chips of uniform fiber length is due to a number ofinterrelated factors. For example, in conventional chippers, if therotating knives are to take a uniform slice from the log to be chipped,the log must be held stationary while a knife is cutting, and it must beadvanced for a uniform distance between each cut. That is, at each cutthe log is drawn into the chipper by the knives and against the drumface, where it remains for the duration of the out, only moving as theknife leaves the piece. short distance from a position of rest and thenstopped at each cut. The inertia of the log may be large, so that theamount of power available for stopping and starting it at each cutlimits the knife striking frequency and the knife velocity to relativelylow values if the essential uni- :5

form chips are to be produced. Surprisingly enough, though, I have foundthat, in a drum chipper, high knife velocities and striking frequenciesproduce substantially superior chips for pulp manufacturing purposes,since at high knife velocities of the order of 4000 F. P. M. (feet perminute) and higher, and striking frequencies of 40 per second andhigher, the knives apparently cut more cleanly and tend to produce opengrained ends to the chips, which are more absorptive and, hence, moreeasily broken down in chemical pulp manufacturing processes.

Accordingly, it has been an object of my invention to provide aself-feeding wood chipper of the drum type in which both high knifevelocity and knife striking frequency may be attained to produce woodchips suitable for pulp manufacture. I have accomplished this resultwhile at the same time producing chips of uniform fiber length, evenfrom heavy large diameter logs, by advancing the log or other materialto be chipped to the knives at a uniform rate rather thanintermittently, thus entirely avoiding the stopping and starting of thelog.

It is a particular feature of my invention that I provide on the drumbetween the knives a feed control means hav- Thus, the entire log mustbe advanced for a I ing a surface configuration which stabilizes the logand holds it firmly in position during its continuous steady advance,Whether with or without a power infeed conveyor, so that the succeedingknife cuts and resulting chip fiber lengths are uniform.

It is a further object of my invention to provide a transverse chipsizing means adapted to split the cut wood into chips, uniform in width,further improving cooking characteristics in the pulping process, sincein this manner a uniform depth of side penetration of cooking liquorshas proven of benefit. This method of transverse chip sizing does notnecessitate employment of serrated edge cutting knives with theirconsequent problems of log instability and lowered production rate, andit has been shown that a chip so split instead of cut exposes the fiberbundles more efficiently for purposes of side penetration than a cutsurface.

Still further objects and features of my invention will be apparent fromthe following description of a preferred embodiment thereof when read inconnection with the drawings, in which:

Fig. 1 is a side elevational view, partly in cross section and brokenaway, of the drum type wood chipper of my invention;

Fig. 2 is an end elevational view, partly in cross-section, of thechipper of Fig. 1;

Fig. 3 is a mathematical illustration of the generation of an idealsurface for the feed control means;

Fig. 4 is a diagrammatic illustration of the wood chipper of Fig. 1showing the generation of a practical surface for the feed controlmeans; and

Figs. 5a and 5b are enlarged views showing the knife and chip sizingmeans of my invention in plan view and side cross-sectional viewrespectively.

Referring to Figs. 1, 2 and 5, the novel drum type wood chipper of myinvention includes a base with up standing side portions 12 havingmounted thereon m-ain bearings 14 adapted rotatably to support a mainshaft 16 driven by any suitable power means (not shown) such as a dieselor electric motor. A curved base portion 18 is provided between saidside portions 12. A generally cylindrical drum 2%, having chipcollecting recesses 22' extending lengthwise of the periphery of saiddrum is mounted fixedly on said shaft 16 so that it may be rotated bysaid shaft about a central axis, end disks 24 preferably being providedon said drum, said drum and said end disks fitting relatively closelywith said curved base portion 18.

One or more peripheral knives 25 (herein shown as four) are mounted onsaid drum 20 by suitable machine bolts 29 adapted to fit into suitablytapped holes in said drum, said knives extending generally lengthwisealong the peripheral face of said drum and preferably parallel to theaxis thereof, although knives having a helicoidal cutting edge may beused if desired. The knives 25 have their cutting edges 26 facingforwardly with respect to their direction of rotation and adjacent aleading face 27 of said knives, the trailing face 28 thereof being at ashorter radial distance from the axis of drum 20 than the cutting edge26, so that the cutting edges of said knives describe a cylindrical pathwhen shaft 16 with drum- 20 is rotated, the portion of the trailing face23 adjacent the cuttting edge 26 being at a slight angle inwardly from atangent to the cylindrical path of said cutting edges, such anglecommonly being of the order of 5 degrees.

The leading face 27 of each of said knives 25 is disposed at shear angleof say 40 to the tangent of the cylinder of rotation of the knifecutting edge 26, and has mounted thereon a chip sizing member 30, saidmember being pressed firmly along the leading face 27 of said knifespaced inwardly from thecutting edge 26 thereof,

the bolts 29 serving to hold said members 30 and knives 25 together. Thechip sizing members 39, as best shown in Figs. a and 5b, comprisemembers extending generally lengthwise of the knives 25, and spaced at adistance from the cutting edge of said knives. The fiat face of each ofsaid members is mounted against a knife leading face 27. The workingface of said chip sizing members has therein extending radially of drum2!) a plurality of grooves 32 with lands 34 therebetween, the bottom ofsaid grooves being at an obtuse angle, say between l00 and 150 degrees,to the leading face 27 of knives 25.

A fixed bed knife 40 is mounted along the forward edge of curved baseportion 18 to cooperate with the cutting edges 26 of knives to sever thechips at the bottom of a log 16, said log being supported and guided bya bed plate 42 mounted forward of bed knife and between base sideportions 12.

In order to advance a log 10 endwise into engagement with said knives25, I have provided a chain conveyor supported by sprockets 52 on shaft54 mounted in suitable bearings 55 on said base portions 12. The shaft54 is driven by gearbox 56 through a sprocket 57 and chain 53 from asprocket 59 on main drive shaft 16, the speed of said chain conveyorbeing in timed relation to the automatic advance of log 10 by knives 25as hereinafter more fully explained.

Preferably and as shown, a log it] is presented to the drum 20 with itsrotating knives 25 along a peripheral lower quadrantal portion only ofthe drum in which the knives 25 are effective to advance the log byreason of the forward component of the motion of said knives in saidportion when the drum- 20 is rotated, for example, with a drum mountedto rotate about a horizontal axis and with a log 10 presented with itsaxis horizontal, a lower forward quadrant only of the drum is used forchipping purposes. If other than horizontal axes are used, the lowerforward quadrant of the drum may be similarly defined by relation to thecommon plane of such axes. For uniformity of chipping it is furtherdesirable that somewhat less than such quadrant be used as illustratedin Fig. 1, wherein the angle of the drum subtended by the log or othermaterial to be chipped as a practical matter should be no greater than80 degrees, preferably about 60 or less. plate 42 and bed knife 49 areraised somewhat above the horizontal tangent to the bottom of thecylindrical knife path, and a guard member 46 is mounted on upstandingbase members 12 across the face of drum 2%, the lower surface of saidguard member 46 being somewhat below the horizontal diameter of thecylindrical path of said knife means.

In order to provide for the essential uniform and continuous advance ofthe log so that the requisite high knife frequencies and velocities maybe employed accord- :1

ing to my invention, I have provided between a knife cutting edge 26 anda next succeeding leading face 27 of said knife means a feed controlmeans externally bounded by a curved surface which is spaced graduallyand progressively inwardly of the cylindrical path defined by thecutting edges of knives 25. Thus such bounding surface extends from acutting edge 26 at a gradually decreasing radial distance from thecentral axis of drum 20 to a next succeeding leading face 27 of a knife25, the inward spacing of said surface at the leading face 27determining the maximum depth of cut of each of said knives, it beingunderstood that the depth of cut of each of said knives should besubstantially equal. Such surface need not extend continuously except asis necessary to provide a firmendwise support for the log 10 or othermaterial as it is advanced by the revolving motion of knives 25. Infact, as in the usual drum chipper, an opening into each of the chipcollecting recesses 22 must be left immediately in advance of a knife 25to provide for the collection of the severed chips until they aredischarged To that end, the base lit) by centrifugal force when theparticular chip recess 22 passes beyond the cut ed surface portion 2.3of the base.

The ideal guiding surface may be best defined mathematically from Fig. 3wherein a quadrant corresponding to that of a four knife chipper isshown. The radius about central axis 0 of the cylindrical path definedby the knife cutting edges is indicated by R, whereas the radius of theideal spiral guiding surface at any point Q is defined by r, 0 being theangle of advance of said radius r from a leading face of a knife on theX axis of Fig. 3. Assuming N knives, and that each knife is to take acut of depth equal to D, the distance S between knife radius R and guidesurface radius r at any point may be expressed in polar coordinates as:

This formula is a general case by which the configuration of the feedcontrol means of the novel chipper of my invention may be accuratelyfound for any given case.

In practice, however, the generation of such ideal surface is bothdifficult and expensive, and I have found that with a chipper employingat least three and preferab'ty four knives, such an ideal spiral guidingsurface may be approximated by a cylindrical surface the axis of whichis parallel to but offset from the central axis of drum 20 and theradius of which is less than that of the path of knife cutting edges 26,as is best illustrated in Fig. 4. Such a surface may be defined by firstdetermining a depth of cut P which will give a desired average length offiber, which average length of fiber will be substantially equal to thevalue D of an ideal surface. Preferably, this is done by assuming anaverage center of a log, say of one-haif the radius R, at which pointthe fiber length of a chip may be assumed as equal to D and in such casethe depth of cut P will be equal to D cos 0, a being 30. The are ofknife periphery between the leading edge of one knife and the leadingedge of a next succeeding knife is then divided into a number of equalincrements of are by means of radii from the center of the drum. Bymeasuring a cumulative distance inwardly from the periphery of the knifecutting edge along each succeeding radius a distance equal to F dividedby the number of segments, a series of points P will be defined. Thecenter a of an are which best approximates the curve through points Pmay then be determined by defining such are as one passing through anythree points P, preferably the points at each end of the quadrant and apoint P midway along the quadrant. The are so determined will have aradius C, less than that of the path of the knife leading edge, andcenter :1 thereof will be displaced from the axis of the drum generallyin the direction toward said first knife trailing face 28. A cylindricalsurface as above defined will provide chips in which the fiber lengthsare substantially uniform within the narrow limits acceptable in pulpmanufacturing processes.

Feed control members 60, with their outer surfaces formed either as anideal spiral surface or as a practical cylindrical surface, are boltedto drum 20 between the knives 25 by suit'abie machine bolts 29 and 52.Bolts 29 serve to retain the leading edge of said members 60 adjacentthe trailing face 28 of a knife 25, as well as to retain said knife 25and its adjacent chip sizing member 30 as hereinbefore described. Bolts62 retain the trailing edges of members 60 adjacent the leading side ofchip collecting recesses 22, thus leaving said recesses open for asufficient distance in advance of knives 25 to retain the chips cutduring a cut across the face of log 10. Both leading and trailing bolts29 and 62 are recessed below the surface of said feed control members60, and the leading bolt 29 may be provided with plug 64 if desired.

As a specific example of a rotary chipper of my inventiou, assuming a30" diameter knife path, four knives (as in Fig. 4), a drum rotationalspeed V of 1100 R. P. M., and a fiber length of A3" at each quarterrevolution. Such dimensions will result in automatic log advance atabout 230 ft./rnin. The knife striking frequency in such specificchipper will be about 73/sec., and the knife speed about 8600 linealft./ min. The fiber length of the chips produced by such machine ingeneral varies no more than about &

The speed v of the conveyor 50 under such circumstances will be equal tothat of log advance or about 230 ft./min., substantially as determinedby the formula when D N V (feet per minute). Thus a 6" diameter conveyordrive sprocket 52 should be rotated at a speed of about 144 R. P. M.

With such a chipper in operation, when the log is advanced far enough byconveyor 50 to be engaged by the knives 25, they act to pull the end ofthe log against the feed control members 60 which cooperate with saidknives to continuously and uniformly advance the log to be chippedendwise in the direction of its length by repeatedly chipping the woodalong a curved surface in a direction transversely and forwardly of itslength until it is entirely reduced to chips. bers 60 simultaneouslystabilize the chipping action and limit the maximum extent and rate ofinfeed by surface contact with log 10 distributed over a major portionof the leading curved infeed end surface of said log. Since the knivescut while the log advances, by this method, a plurality of knives may beused efficiently, such that two or more knives may be cutting in the logat the same time, thus permitting the use of this stabilizing featuretermed multi-knife action. The release of knife pull between strikescauses rebounding reflex action. How ever, it has been found that thereis a minimum frequency of strike of about 40 strikes per second whereinthe same stabilizing influence may be found with but one knife in thelog of a time. For the purposes of clean cutting action of the knives,even on thin or light material, the chipping velocity of the knivesshould be at least 4000 feet per minute. Preferably such strikefrequency should be 60 to 100 strikes per second and knife velocity5,000 to 10,000 lineal feet per minute. I

In cooperation with the normal formation of chfp cards or sheets of agiven thickness, the chip sizing members act on the cut card sheet tosplit it into relatively narrow and uniform widths, the change ofdirection produced by the angle between the bottom of the grooves 32 andknife leading face 27 serving to press tiiz: cards downwardly over thesharp lands, thus in effect splitting the cards longitudinally thereof.

The chips so formed are held in the chip recesses 22 until such recessespass beyond the curved base portion 18, whereupon they will bedischarged fromsaid recess'.";

by centrifugal force in the usual manner.

Though it is presently preferred that the wood feed be substantiallyhorizontal with the resultant cutting being done in a lower forward drumquadrant, it will be understood that the wood feed may be other thanhorizontz. (i. e., inclined or even vertical) so long as the relativepresentation made to the drum is such that the forward component ofknife motion tends to advance the wood to be chipped and aid it'suniform presentation to the knives during chipping.

Thus it will be seen that there is provided a drum chipper whichcontinuously and uniformly advances the material to be chipped toprovide high quality chips of uniform fiber length.

I claim:

1. A wood chipper of the generally cylindrical drum type rotatable abouta central axis, including peripheral knife means mounted on said drumand extending gen- The feed control memerally lengthwise thereof, saidknife means having an outer forwardly facing cutting edge and a trailingface extending rearwardly therefrom at an angle inwardly from a tangentto the path of said cutting edge, feed control means positioned on saiddrum between a trailing edge and a next succeeding leading face of saidknife means, the external guiding surface of said feed control meansbeing defined by a curved surface extending between said cutting edge ofsaid knife means at a gradually decreasing radial distance from saidcentral axis to said next succeeding leading face of said knife meansand controlling the maximum depth of chipping cut, chip collecting meanson said drum between said feed control means and said next succeedingleading face of said knife means, and guide means adapted to presentpieces of wood to be chipped endwise to said knife means and in contactwith said feed control means along a peripheral portion of said drum inwhich said knife means is effective to advance said material by reasonof the forward component of the knife motion in said portion to the endthat said material will be continuously and uniformly advanced by thecooperating knife and feed control means.

2. A wood chipper of the generally cylindrical drum type rotatable abouta central axis, including a plurality of peripheral knives mounted onsaid drum and extending generally lengthwise thereof, said knives havingouter forwardly-facing cutting edges, respectively, parallel to oneanother and having trailing faces extending rearwardly therefrom at anangle inwardly from a tangent to the path of said cutting edges, feedcontrol means positioned on said drum between a trailing face and a nextsucceeding leading face of said knives, the external guiding surface ofsaid feed control means being defined by a curved surface extendingbetween said cutting edge of said knives at a gradually decreasingradial distance from said central axis to said next succeeding leadingface of said knives and controlling the maximum depth of chipping cut,chip collecting recesses in said drum between said feed control meansand said next succeeding leading face of said knives and extendingradially inwardly of the external surface of said feed control means,and guide means adapted to present pieces of wood to be chipped endwiseto said knives and in contact with said feed control means along aperipheral portion of said drum in Which said knives are effective toadvance said material by reason of the forward component of the knifemotion in said portion to the end that said material will becontinuously and uniformly advanced by the cooperating knife and feedcontrol means.

3. A wood chipper as claimed in claim 2 in which the curved surfaceexternally bounding said feed control means is defined by a cylindricalsurface of radius less than that of the radial distance from saidcentral axis to the cutting edge of said knives and having its axis displaced from the central axis.

4. A wood chipper as claimed in claim 1 in which said guide meansincludes a lower bed knife raised with respect to a horizontal tangentto the cylindrical path of said knives and an upper guard means loweredwith respect to the horizontal diameter of said cylindrical path topresent pieces of wood to be chipped to less than a quadrantal portionof said drum.

References Cited in the file of this patent UNITED STATES PATENTS233,765 Innis Oct. 26, 1880 747,827 Wolfinger Dec. 22, 1903 829,927Luther Aug. 28, 1906 1,473,545 Collier Nov. 6, 1923 1,543,919 HabighorstJune 30, 1925 2,073,911 Tower Mar. 16. 1937 2,269,352 Bacon Jan. 6, 1942

